1. Field of the Invention
The present invention relates to a magnetic material and an antenna device.
2. Description of the Related Art
The frequency band of electric waves used for current mobile communication terminals is in a high-frequency region of at least 100 MHz. Thus, much attention has been paid to electronic parts and substrates which are useful in this high-frequency region. Mobile communications and satellite communications use electric waves of a high-frequency region of a GHz-band.
To cope with electric waves in such a high-frequency region, it is necessary to reduce energy loss and transmission loss in electronic parts. For example, with antenna devices essential for mobile communication terminals, electric waves generated by an antenna may suffer transmission loss during a transmission process. The transmission loss may be consumed in the electronic parts and a substrate as thermal energy to cause the electronic parts to generate heat. Further, the transmission loss cancels electric waves to be transmitted to an external device. Consequently, powerful electric waves need to be transmitted, thus preventing the effective use of power. Moreover, communications with electric waves at a minimized level have been desired.
High-frequency devices using an insulating substrate with a high magnetic permeability can catch generated electromagnetic waves in the substrate. This makes it possible to prevent electromagnetic waves from reaching electronic parts or a printed circuit board. That is, power can be saved.
Normal high-magnetic-permeability materials include metal or alloy composed of Fe or Co and oxides of Fe and Co. A high-magnetic-permeability material of metal or alloy suffers a significant transmission loss at an increased electric wave frequency owing to eddy currents. This makes it difficult to use such a material as a substrate. On the other hand, if a magnetic substance of an oxide typified by ferrite is used as a substrate, high resistance offered by the magnetic substance inhibits transmission loss. However, because of a resonant frequency of several hundred MHz, transmission loss caused by resonance becomes significant at high frequencies, making it difficult to appropriately use the device. Thus, a material for the substrate has been desired to be an insulating high-magnetic-permeability member which can also be used for electric waves of high frequencies and which suffers a minimized transmission loss.
As an attempt to produce such a high-magnetic-permeability member, high-magnetic-permeability nano-granular materials have been produced using a thin film technology such as sputtering. These materials have been confirmed to exhibit excellent properties even in a high-frequency region. However, with the granular structure, it is difficult to increase the volume percentage of magnetic particulates with high resistance maintained.
On the other hand, JP-A 2004-95937(KOKAI) discloses a composite magnetic material comprising an inorganic insulating base material composed of an oxide, a nitride, or a mixture of the oxide and the nitride, and a columnar structure with a single magnetic domain buried in the inorganic insulating base material and composed of a pure metal such as Fe, Co, or Ni or an alloy containing at least 20 wt % of the pure metal.